A mixture of chromium and zinc weighing .362 g was reacted with an excess of hydrochloric acid.

After all the metals in the mixture reacted 225 mL of dry hydrogen gas was collected at 27 C and 750 torr.
Determine the mass percent Zn in the metal sample. [Zinc reacts with hydrochloric acid to produce Zinc chloride and hydrogen gas;
chromium reacts with hydrochloric acid to produce chromium (III) chloride and hydrogen gas.]

Let Y = grams Zn
Z = grams Cr
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Y+Z=0.362 g
Y(MM Zn/MM H2) + Z(2MM Cr/3MM H2) = grams hydrogen.
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Note: MM stands for molar mass. 2MM and 3MM stands for 2xmolar mass and 3xmolar mass respectively.
To find grams hydrogen:
225 mL at 27C (300 Kelvin) and 750 torr will correct to STP as zz mL at 273 K and 760 torr. Then change to liters and L/22.4 = mols and mols x molar mass hydrogen (which is 2) will convert to grams.

Then solve the above set of simultaneous equations for Y to obtain grams Zn.
Then grams (Zn/0.362)x100 = % Zn

Check my thinking. Check my work.

The second equation in the set comes from the balanced equations.
Zn + 2HCl ==> H2 + ZnCl2
2Cr + 6HCl ==> 3H2 + 2CrCl3

I hope this helps.

your not smart

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I give you this double-bladed light saber to help you in this question.

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Well, let's try and solve this problem with a little bit of clown humor, shall we?

Okay, so let's start by giving Y the role of grams Zn and Z the role of grams Cr. Now, these two metals are so inseparable, they add up to a total weight of 0.362 grams! They're like a double act, always together on the stage.

Now, let's move on to the hydrogen gas. This gas is so dry, it could be a stand-up comedian! It was collected in a whopping 225 mL, at a cool 27 degrees Celsius and 750 torr. But let's give it a makeover, converting it to STP conditions. We'll make it go from mL to zz mL (a special clown unit), and adjust the temperature and pressure to make it feel right at home at 273 K and 760 torr. It will then change from mL to liters, because it likes breathing freely. Finally, we'll divide it by 22.4, because 22.4 liters of gas at STP make a mole, as any gas will tell you.

Now, we have our mols of hydrogen gas, which weighs about 2 grams per mole. Of course, this hydrogen gas is a real lightweight, just like a clown balancing on a ball. And that's grams, not clown grams, mind you.

Now, it's time to solve our simultaneous equations to find out the grams of Zn. Once we have that, we can find the percent Zn by dividing it by 0.362 and multiplying it by 100.

So there you have it, a clown's take on solving this chemistry problem. I hope it made you smile, and I promise, no clown noses were harmed in the making of this answer!

Your thinking and approach are correct. In order to find the mass percent of zinc in the metal sample, you need to follow these steps:

1. Assign variables: Let Y represent the grams of zinc (Zn) and Z represent the grams of chromium (Cr) in the mixture.
2. Write the equation Y + Z = 0.362 g, representing the total mass of the mixture.
3. Write the equation Y(MM Zn/MM H2) + Z(2MM Cr/3MM H2) = grams of hydrogen. This equation comes from the balanced chemical equations for the reactions of zinc and chromium with hydrochloric acid.
- MM Zn represents the molar mass of zinc.
- MM Cr represents the molar mass of chromium.
- MM H2 represents the molar mass of hydrogen.
4. Calculate the grams of hydrogen produced. To do this, you need to first convert the given conditions of 225 mL, 27°C, and 750 torr to standard temperature and pressure (STP).
- Convert 225 mL at 27°C (300 Kelvin) and 750 torr to STP: Use the ideal gas law or gas laws to convert the volume, temperature, and pressure accordingly.
- Convert mL to L and adjust temperature to 273 K and pressure to 760 torr.
- Then, divide the volume by 22.4 L/mol to get moles of hydrogen gas produced.
- Multiply the moles by the molar mass of hydrogen (2 g/mol) to obtain the grams of hydrogen.
5. Solve the set of simultaneous equations Y + Z = 0.362 g and Y(MM Zn/MM H2) + Z(2MM Cr/3MM H2) = grams of hydrogen to obtain the grams of zinc (Y).
6. Calculate the mass percent of zinc by dividing the grams of zinc (Y) by the total mass of the mixture (0.362 g) and multiplying by 100.

Make sure to use the correct molar masses and units when performing calculations.

By following these steps, you will be able to determine the mass percent of zinc in the metal sample.